ADHD is a chronic developmental disorder characterized by issues associated with attention, inhibiting irrelevant stimuli, and/or focusing too intensely on specific stimuli to the extent that this interferes with being productive at work or school. This disorder has been found to be present in 3 to 10% of children and 1 to 6% of adults and 50-66% of children continue to be affected by ADHD issues into adulthood (Spencer et al., 2002; Daley, 2004). There is a high risk of cigarette smoking and substance abuse in children with ADHD. Children growing up with ADHD can face academic impairments, social dysfunction and poor self-esteem.
The Diagnostic and Statistical Manual (DSM) IV defines five subtypes: predominately hyperactive/impulsive where patients shows 6 or more hyperactive/impulsive symptoms and fewer than 6 inattentive symptoms; predominately inattentive type with 6 or more inattentive symptoms and fewer than 6 hyperactive/impulsivity symptoms; ADHD combined with 6 or more hyperactive/impulsivity and inattentive symptoms; partial remission where patient previous met criteria but currently only displays some impairing symptoms; and ADHD not otherwise specified where full criteria are not currently met and it is unclear that criteria were met in the past (Murphy & Adler, 2004). Complications of diagnosis of especially adults include that there is no diagnostic test for ADHD, other comorbid conditions, clinical subjective judgment is needed to determine interference of least 2 areas of life and the establishment of childhood onset may not be possible. Conditions that can either mimic ADHD symptoms or are comorbid with ADHD include conduct disorder, oppositional defiant disorder, major depressive disorder, anxiety disorder, bipolar disorder, learning disabilities and substance abuse (Spencer et al., 2002; Daley, 2004).
There is no clearly defined single etiology of ADHD. The pathophysiology of ADHD may be impacted by genetics, prenatal and perinatal risk factors and neurobiological deficits. Cigarette and alcohol exposure increases the risk along with a 75% genetic component (Spencer et al., 2002). Areas of the brain involved in attention including the prefrontal cortex where dopamine and norepinephrine receptors predominate have been documented to be smaller and less active in ADHD patients compared to control implicating the catecholamines, dopamine and norpinephrine (Spencer et al., 2002; Grund et al., 2006; Rader et al., 2009).
The treatment of ADHD has been primarily with stimulant medication including methylphenidate, dextroamphetamine and mixture of stimulants as first-line treatment (Rader et al., 2009). Stimulant medications do not necessarily last for 24 hours even with extended release formulations. Thus, stimulants need to be taken 2 to 3 times daily leading to compliance issues (Daughton & Kratochvil, 2009). However, compliance is improved with the extended release formulations by reducing stigma of taking medication at school but side effects continue until later in the day and tend to be expensive. Stimulants have the potential for abuse and may not be ideal for comorbid conditions including tic disorders (Spencer et al., 2002). In addition, there is a need to monitor children for the impact of stimulant medication on growth (Daley, 2004) and for blood pressure and heart rate changes (Daughton & Kratochvil, 2009). Other side effects include appetite suppression, weight loss, abdominal pain, headache, irritability, cardiovascular effects, insomnia, skin irritation and rash (Rader et al., 2009).
Nonstimulant treatments have also been effective with advantages of longer duration of use, less abuse potential and treatment of comorbid conditions over stimulant medications (Daley, 2004). Atomoxetine, considered a second-line treatment, shows high selectivity for the presynaptic norepinephrine transporter and promise in children and adults with ADHD with long lasting therapeutic effects and less abuse potential (Rader et al., 2009; Daughton & Kratochvil, 2009). However, the efficacy that atomoxetine achieved was not up to the level of the stimulants. In addition, efficacy onset is gradual and there is a risk of suicidal ideation, jaundice and potential interaction with CYP 2D6 substrates.
Third-line treatments include tricyclic antidepressants, bupropion, and alpha2 agonists (Rader et al., 2009). Tricyclic antidepressants with actions on catecholamine reuptake have been prescribed for ADHD but TCA action is not selective and adverse effects include dry mouth, blood pressure changes, weight gain, cardiac conduction delays and constipation. Buproprion, antidepressant with dopamine and norpinephrine agonist effects, appears to be effective in ADHD but there is a higher risk of drug-induced seizures albeit at higher dose levels, previous history of seizures and eating disorder (Daley, 2004). Side effects of clonidine and guanfacine, alpha2 agonists, are drowsiness, dizziness, dry mouth and orthostatic hypotension but these drugs are useful for patients with conduct disorder and help counteract insomnia and appetite suppression caused by stimulants (Rader et al., 2009). Selective serotonin reuptake inhibitors have been investigated for ADHD but demonstration of efficacy has not been promising (Spencer et al., 2002).